The invention relates to light-emitting diode (“LED”) devices, and more particularly to LED devices having a plurality of LEDs arranged in an array for use in flash applications.
An LED is a semiconductor device capable of emitting light when an electric current flows through it. LEDs are used in many applications, such as electronic displays, traffic signals, and video signs. LEDs emit monochromatic light, i.e., the wavelength of light emitted by an LED falls within a narrow range, typically about 20-50 nanometers (“nm”). However, different types of LEDs emit different wavelengths (colors) of light. LEDs are often characterized by the full-wave-half-maximum (“FWHM”), which is the spread of wavelength emitted by an LED at 50% of maximum radiation power.
FIG. 1 is a plot of a typical spectral emission of an LED illustrating the LED's FWHM. The output is shown in arbitrary units of light radiation, and the FWHM is the difference between λ1 and λ2.
LEDs are also used in appliances such as mobile phones, personal digital assistants (“PDAs”), and digital cameras. LEDs are used in mobile camera phones in the flash module. In this application, an LED module acts as an illumination source and is activated when a picture is taken when there is insufficient ambient light, or when back-fill lighting is desired. At least three LEDs are typically used in a flash module, a red LED (i.e., an LED emitting red light), a green LED, and a blue LED.
FIG. 2 shows three plots of three LEDs in arbitrary units versus wavelength. A first plot 20 shows the output from a blue LED, a second plot 22 shows the output from a green LED, and a third plot 24 shows the output from a red LED. The combined spectral emission of these three LEDs is not ideal because it is peaky and discontinuous. A gap 23 occurs between the second plot 22 and the third plot 24. Peaky, discontinuous spectral emission from a flash module can result in poor image quality, such as unfaithful reproduction of the color of the subject. Hence, an LED flash module providing better color image quality is desirable.